1. Field of the Invention
The present invention relates to transmission of data in a communications system. In particular the present invention relates to discontinuous transmission/reception of data in a communications system.
2. Description of the Related Art
A communication system can be seen as a facility that enables communication sessions between two or more entities such as user equipment and/or other nodes associated with the communication system. The communication may comprise, for example, communication of voice, data, multimedia and so on. Communication systems providing wireless communication for user equipment are known. Cellular communication systems are configured to have a cell structure, and typically they support communication with user equipment changing locations (mobile users). The support for communications for mobile users may include support for handing existing connections from one cell to another cell. At least routing of calls or communications for a mobile user in a new cell is typically supported in cellular systems. Some examples of a cellular system are the Global System for Mobile Telecommunications (GSM) and General Packet Radio Service (GPRS). GPRS provides packet-switched data services and utilizes the infrastructure of a GSM system. Further examples of a cellular system are third generation telecommunication systems, which support both packet-switched and circuit-switched transfer. The Wideband Code Division Multiple Access (WCDMA) system is one example of a third generation cellular telecommunication system.
Traditionally communications systems have been circuit-switched systems, where a certain amount of resources is reserved for a connection/call continuously irrespective of the need of transmitting data at a particular moment in time. The reserved amount of resources may be, for example, a dedicated channel. The channel, in turn, may be defined for example by a certain slot in successive time frames in a time division multiplex system, a certain frequency in a frequency division multiplex system or a certain channelization code in a code division multiplex system.
In this allocation scheme, resources that are announced to a given communications device are occupied and are not available to any other communications devices, before the allocation is released. The resource occupation is maintained, even if the given communications device has actually no data to transmit or to receive. For allocating transmission resources in a more efficient way, it is possible to take into account the actual need for transmission capacity when allocating transmission resources. For time-critical data (for example, a voice call) resources may be allocated on a continuous basis, but less time critical data may be buffered until there are free transmission resources. In the novel communication systems the available bandwidth and symbol rate is huge compared to the traditional ones. Thus, any fixed reservation of resources, which are actually not in use, will cause unnecessary loss of efficiency.
In novel communication systems, due to their inherent large transmission capacity, it is possible to share the communication medium efficiently among many communications devices. The communications devices typically monitor the shared medium for transmitting and receiving information most efficiently. The communications systems work by random access and collision detection or alternatively the allocation of resources is given in an explicit way by signalling.
When transmitting information on a shared medium, the communications devices typically need to know exactly which pieces of information are intended for them to receive and which pieces of transmission resources are intended for them to transmit. This is typically done by exchanging explicit allocation information between the communications system and the communications devices. The allocation information may be transmitted on a shared signalling channel or using an associated signalling channel. High Speed Downlink Packet Access in the WCDMA system, for example, uses a high-capacity shared data channel for downlink data transfer and a low-capacity shared signalling channel for informing the communications devices about the specific resource allocations on the shared data channel. In a Wireless Local Area Network, each data packet header contains identifiers of the communications device to indicate which device this data packet is addressed to and which device needs to decode it. Thus, all communications devices need to monitor and process the headers of all data packets for being able to receive data addressed to it.
When a communications device is listening to a shared medium, it needs to monitor allocation information continuously or at least very frequently for every transmission unit for determining whether it should receive data in the downlink direction or whether it could transmit data in the uplink direction. Thus allocation information needs to be monitored continuously at least once per transmission unit, although the actual data transmission and/or reception occurs in a discontinuous manner. Continuous monitoring and decoding of potential presence of allocation information consumes power. Especially for wireless communications devices, power consumption is a critical factor.
Embodiments of this invention aim to provide an efficient solution for discontinuous transmission and/or reception.